Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Contingency [Line Items]
U.S. federal tax statutory rate (percent)	35.00%	35.00%	35.00%
Net operating loss	$ 411,100,000
Current income tax	0	$ (9,000)	$ 134,000
Deferred tax asset related to net operating loss carryforwards	228,279,000	121,248,000
Unrealized excess tax benefits from stock-based compensation	4,000,000
Unrecognized tax benefits	0
Deferred tax liability, current		$ 0
Federal
Income Tax Contingency [Line Items]
Net operating loss	620,700,000
Valuation allowances related to operating loss carryovers	600,000
Stock-based compensation related to unrealized excess tax benefits	10,600,000
State
Income Tax Contingency [Line Items]
Net operating loss	505,100,000
Valuation allowances related to operating loss carryovers	800,000
Stock-based compensation related to unrealized excess tax benefits	$ 8,600,000